Assessing the Impact of Wetland Conversion to Unregulated Urban Development on Flood Risk: A GIS-Based Analysis of the Meda Ela and Pinga Oya Catchments in Kandy District

Urban flooding is a significant challenge facing the city of Kandy, situated in the central highlands of Sri Lanka. This study focuses on assessing the impact of wetland conversion to unregulated urban development on flood risk in the Meda Ela and Pinga Oya catchments in the Kandy district, utilising the Geographic Information System (GIS). The main objectives of this research involve a comprehensive examination of temporal changes in land use and land cover (LULC), with a particular emphasis on the sealing of wetlands (paddy lands) and their implications for urban flooding. To achieve these objectives, the study employs secondary data, including land use data from the Survey Department of Sri Lanka spanning the years 1999 to 2020, elevation data from USGS, built-up area data from ESA WorldCover, and historical flood events from different secondary sources. The research methodology encompasses, (1) reclassification analysis to identify wetlands, (2) zonal analysis to quantify wetland extents, (3) terrain analysis to spot low-lying areas near main streams, and (4) Multicriteria Decision Making (MCDM) to delineate a flood risk model using ArcGIS 10.8.2. The findings reveal a significant reduction in wetland areas and a corresponding expansion of built-up regions during the considered period in catchment scale and corridor scale. In the Meda Ela catchment, wetlands decreased from 44.66 hectares to 27.53 hectares, and built-up areas increased from 20.99 hectares to 196.62 hectares. Similarly, in the Pinga Oya catchment wetlands decreased from 1995.23 hectares to 1642.57 hectares, with the expansion of built-up areas from 2.25 hectares to 15.63 hectares. Correspondingly, the temporal growth of wetlands sealing led to a rise in flood events in both catchments. MCDM-based flood risk model indicated specific areas, like Kandy City to Suduhumpola reach in the Meda Ela and Akurana to Ambathenna in the Pinga Oya catchments, which are highly vulnerable to flooding due to their basin characteristics. Consequently, this study highlights the need for sustainable flood mitigation strategies by preserving existing wetlands and practicing resilience in systematic urban development.